Method of and apparatus for manufacturing multi-layer optical information recording medium

ABSTRACT

A transfer layer on a surface of a mold has a thickness distribution along the radius direction that the layer is thick in an inner round portion but is gradually thinner toward an outer round portion. An adhesive layer is formed between a surface of a signal substrate which bears a signal recording film and the mold which seats the transfer layer. The adhesive layer has a thickness distribution that the layer is thin in an inner round portion but is gradually thicker toward an outer round portion. Since the thickness distributions along the radius direction of the transfer layer and the adhesive layer are opposite to each other, the thickness distribution of an isolation layer which comprises the two layers is uniform.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus formanufacturing a multi-layer optical information recording medium onwhose one surface recording and reproduction are performed and whichcomprises an isolation layer between a plurality of signal recordinglayers.

2. Related Art of the Invention

As a high-density optical information recording medium, a multi-layeroptical information recording medium, such as a DVD of thesingle-side/dual-layer reproducing format, has been proposed whichcomprises a plurality of signal recording surfaces along the thicknessdirection. For example, a DVD of the single-side/dual-layer reproducingformat has a structure that a translucent reflection layer of gold,silicon or the like is formed oh the information recording surface ofone of two substrates and a conventional reflection layer of aluminum orthe like is formed on the information recording surface of the other oneand that the reflection layers are bonded in such a manner that theseinformation recording surfaces are directed toward the inner side.

Further, for an improvement in surface recording density per layer, ahigh-density optical information recording medium has been proposedwhich uses a blue-violet laser source (whose wavelength is about 400 nm)and a high-NA lens and comprises a thin recording/reproduction sidetransparent cover layer whose thickness is as thin as 0.1 mm. Thishigh-density optical information recording medium has a structure that asignal guide groove or pit is formed in a surface of a thick signalsubstrate, a recording multi-layer film which is rewritable is formed onthis, and a transparent cover layer is formed further on this. Even ahigh-density optical information recording medium of this thintransparent cover layer type may be modified to comprise two signalrecording surfaces. The following is one example of a method offabricating the same.

(1) On a thick substrate which seats a rewritable recording multi-layerfilm whose surface comprises guide grooves or pits representing signals,an isolation layer is further formed using an UV curable resin, and on asurface of the isolation layer, second-layer guide grooves or pitsrepresenting signals are formed.

(2) On the second-layer guide grooves or pits representing signals, atranslucent recording multi-layer film which is rewritable is formed.

(3) A thin recording/reproduction side transparent cover layer whosethickness is as thin as 0.1 mm is formed.

As a specific fabrication method (See Japanese Patent ApplicationLaid-Open Gazette No. 2002-260307), using a plastic mold 2100 for thestep (1) above, the signal guide grooves or pits on the mold 2100 arecovered and a first UV curable resin is applied and hardened. Followingthis, using a second UV curable resin which has a different property asan adhesive layer, the substrate seating a first signal recording layer2106 and the hardened first UV curable resin are bonded together, andthe mold 2100 is peeled off from the second UV curable resin afterhardening. In this manner, an isolation layer 2110 is formed from thefirst UV curable resin and the second UV curable resin. When such amethod is used, it is possible to fabricate a multi-layer opticalinformation recording medium by laminating one signal recording layer2106 and further a plurality of signal recording layers 2106 on a thicksignal substrate 2105 which is rigid through the isolation layer 2110.The entire disclosure of the document mentioned above is incorporatedherein by reference in its entirety.

However, it is necessary that the thickness of the isolation layer 2110which exists between the signal recording layers 2106 is uniform in themulti-layer optical information recording medium. The uniform thicknessof the isolation layer 2110 results in a constant level of influence ofreflected light from one signal recording layer 2106 which is eitherbefore or after the isolation layer 2110 upon the other signal recordinglayer 2106 which is either before or after the isolation layer 2110during recording or reproduction. A variation in reflected light fromthis signal recording layer 2106 creates a disturbance component in areproduction signal, which deteriorates S/N. On the contrary, when thethickness of the isolation layer 2110 is uniform, disturbance from thissignal recording layer 2106 becomes constant, and therefore, recordingor reproduction becomes stable and the quality of the reproductionsignal improves.

FIG. 12 is drawings which show a change with time in dripping amount ofan UV curable resin onto the signal substrate 2105 or the mold 2100 andthe number of revolutions of the signal substrate 2105 or the mold 2100in a condition that the UV curable resin is being dripped duringfabrication of a conventional multi-layer optical information recordingmedium. As shown in FIG. 12, according to a conventional manufacturingmethod, the UV curable resin is dripped in the vicinity of a centralportion of the signal substrate 2105 or the mold 2100, and after the endof dripping, the signal substrate 2105 or the mold 2100 is rotated andthe UV curable resin is stretched from the area close to the centralportion of the signal substrate 2105 or the mold 2100 toward the outerside owing to the resulting centrifugal force.

When such a manufacturing method described above is used, because of thecentrifugal force resulting from the rotations of the mold 2100 or thesignal substrate 2105, the thickness of the UV curable resin becomesthicker toward the outer side than toward the center side of the mold2100 or the signal substrate 2105. Hence, as shown in FIG. 13, thethickness of the isolation layer 2110, too, tends to become thickertoward the outer side from the center side of the isolation layer 2110which is formed by joining UV curable resins which have differentproperties from each other. Thus, the S/N ratio of a multi-layer opticalinformation recording medium according to the conventional fabricationmethod is not satisfactory as described above.

SUMMARY OF THE INVENTION

In light of the problems with the conventional fabrication methoddescribed above, the present invention aims at providing a method of andan apparatus for manufacturing a multi-layer optical informationrecording medium which permits to stably record in signal recordinglayers which are disposed on the both sides of an isolation layer,stably reproduce from the signal recording layers and obtain anexcellent signal.

The 1^(st) aspect of the present invention is a method of manufacturinga multi-layer optical information recording medium on whose one surfacerecording and reproduction are performed and which comprises anisolation layer between a plurality of signal recording layers,comprising the steps of:

(a) forming an n+1^(−th) layer adjacent to a surface on a mold in whichthere is a signal recording area which contains at least one of a guidegroove and a pit; and

(b) forming an n^(−th) layer adjacent to a signal substrate whichcomprises said signal recording layers,

wherein said isolation layer is formed by joining said n+1^(−th) layerand said n^(−th) layer, and

a thickness distribution along the radius direction of at least one ofsaid n+1^(−th) layer and said n^(−th) layer is generated or controlledbased on a thickness distribution along the radius direction of theother one of said n+1^(−th) layer and said n^(−th) layer.

The 2^(nd) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the1^(st) aspect, wherein said n+1^(−th) layer and said n^(−th) layer areeach formed so as to have predetermined thickness distributions, and

the thickness distribution along the radius direction of said at leastone layer is controlled considering the thickness distribution along theradius direction of the other layer.

With the method of manufacturing a multi-layer optical informationrecording medium according to the first or the second inventiondescribed above, since the radius-direction thickness distribution ofeither one of the n+1^(−th) layer and the n^(−th) layer is controlledconsidering the radius-direction thickness distribution of the otherone, it is possible to control a thickness distribution of the isolationlayer which comprises the both and makes the thickness distributionuniform. This allows to stably record in and reproduce from the signalrecording layers which are disposed on the both sides of the isolationlayer, and hence, to obtain an excellent signal.

The 3^(rd) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the1^(st) aspect or the 2^(nd) aspect, wherein a thickness distributionalong the radius direction of said isolation layer is substantiallyuniform.

With the method of manufacturing a multi-layer optical informationrecording medium according to the third invention described above, sincethe radius-direction thickness distributions of both the n+1^(−th) layerand the n^(−th) layer are controlled, it is possible to control athickness distribution of the isolation layer which comprises the bothand makes the thickness distribution uniform. This allows to stablyrecord in and reproduce from the signal recording layers which aredisposed on the both sides of the isolation layer, and hence, to obtainan excellent signal.

The 4^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the1^(st) aspect, further comprising a step of peeling said mold off fromsaid n+1^(−th) layer.

The 5^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the1^(st) aspect, wherein the thickness distribution along the radiusdirection of said n+1^(−th) layer is that the layer is thinner in anouter round portion than in an inner round portion of said mold, whilethe thickness distribution along the radius direction of said n^(−th)layer is that the layer is thicker in an outer round portion than in aninner round portion in said signal substrate. Using such a manufacturingmethod above, it is possible to ensure that the isolation layer whichcomprises the n+1^(−th) layer and the n^(−th) layer is uniform.

The 6^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the5^(th) aspect, wherein said n+1^(−th) layer is of a radiation curablematerial, and said step (a) comprises a step of dripping said radiationcurable material onto said inner round portion of said mold or saidinner round portion within said n^(−th) layer of said signal substrateand a step of rotating said mold or said signal substrate to which saidradiation curable material has been dripped.

The 7^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the6^(th) aspect, wherein said step of rotating said mold or said signalsubstrate to which said radiation curable material has been dripped isfollowed by a step of superposing said mold and said signal substrateone atop the other in such a manner that said n+1^(−th) layer ispositioned on the inner side, and further by a step of emittingradiation and accordingly irradiating said radiation curable material.

The 8^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the6^(th) aspect, wherein said step (a) comprises a step of dripping saidradiation curable material onto said inner round portion of said mold orsaid inner round portion within said n^(−th) layer of said signalsubstrate and a step of rotating said mold or said signal substrate towhich said radiation curable material has been dripped.

The 9^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of anyone of the 6^(th) aspect through the 8^(th) aspect, wherein portions ofsaid step of dripping said radiation curable material onto said innerround portion of said mold or said inner round portion within saidn^(−th) layer of said signal substrate and said step of rotating saidmold or said signal substrate to which said radiation curable materialhas been dripped are executed simultaneously. Using such a manufacturingmethod above, it is possible to easily control the thicknessdistribution along the radius direction of the n+1^(−th) layer.

The 10^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of anyone of the 6^(th) aspect through the 8^(th) aspect, wherein said mold orsaid signal substrate is rotated while dripping said radiation curablematerial onto said inner round portion of said mold or said inner roundportion within said n^(−th) layer of said signal substrate.

The 11^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of anyone of the 6^(th) aspect through the 8^(th) aspect, wherein beforedripping said radiation curable material onto said inner round portionof said mold or said inner round portion within said n^(−th) layer onsaid signal substrate, in the event that there is a center holeapproximately at the center of said mold or said n^(−th) layer of saidsignal substrate, said center hole is capped with a lid and saidradiation curable material is then dripped from above said lid. Usingsuch a manufacturing method above, it is possible to easily control thethickness distribution along the radius direction of the n+1^(−th)layer.

The 12^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the1^(st) aspect, wherein the thickness distribution along the radiusdirection of said n+1^(−th) layer is thicker in an outer round portionthan in an inner round portion of said mold, while the thicknessdistribution along the radius direction of said n^(−th) layer is thinnerin an outer round portion than in an inner round portion in said signalsubstrate. Using such a manufacturing method above, it is possible toensure that the isolation layer which comprises the n+1^(−th) layer andthe n^(−th) layer is uniform.

The 13^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the12^(th) aspect, wherein said n^(−th) layer is of a radiation curablematerial, and said step (b) comprises: a step of dripping said radiationcurable material onto said inner round portion within said n+1^(−th)layer of said mold or said inner round portion of said signal substrate;a step of rotating said mold or said signal substrate to which saidradiation curable material has been dripped; a step of superposing saidmold and said signal substrate one atop of the other after the rotationsin such a manner that the surface coated with said radiation curablematerial is directed toward the inner side; and a step of emittingradiation and accordingly hardening said radiation curable material.Using such a manufacturing method above, it is possible to easily bondthe mold seating the n+1^(−th) layer with the signal substrate.

The 14^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the13^(th) aspect, wherein portions of said step of dripping said radiationcurable material onto said inner round portion of said mold or saidinner round portion of said signal substrate and said step of rotatingsaid mold or said signal substrate to which said radiation curablematerial has been dripped are executed simultaneously. Using such amanufacturing method above, it is possible to easily control thethickness distribution along the radius direction of the n^(−th) layer.

The 15^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the14^(th) aspect, wherein the rotations are effected while dripping saidradiation curable material onto said inner round portion of said mold orsaid inner round portion of said signal substrate.

The 16^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of anyone of the 13^(th) aspect through the 15^(th) aspect, wherein beforedripping said radiation curable material, in the event that there is acenter hole approximately at the center of said mold or said signalsubstrate, said center hole is capped with a lid and said radiationcurable material is then dripped from above said lid. Using such amanufacturing method above, it is possible to easily control thethickness distribution along the radius direction of the n^(−th) layer.

The 17^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the7^(th) aspect or the 13^(th) aspect, wherein said step of superposing insuch a manner that the surface of said mold or said signal substratecoated with said radiation curable material is directed toward the innerside is executed under a reduced pressure. Using such a manufacturingmethod above, it is possible to prevent air bubbles from getting mixedinto the isolation layer.

The 18^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the5^(th) aspect or the 12^(th) aspect, wherein said n+1^(−th) layercontains a pressure-sensitive adhesive which hardens when irradiatedwith radiation. Such a manufacturing method above realizes easy controlof the thickness distribution since the viscosity of thepressure-sensitive adhesive is high, and ensures reliable transfer of asignal from the mold.

The 19^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the5^(th) aspect or the 12^(th) aspect, wherein said n^(−th) layer containsa pressure-sensitive adhesive. Such a manufacturing method aboverealizes easy control of the thickness distribution of the n^(−th) layersince the viscosity of the pressure-sensitive adhesive is high.

The 20^(th) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the5^(th) aspect, wherein said n^(−th) layer is of a radiation curablematerial, and said step (b) comprises: a step of dripping a radiationcurable material for adhesion which is for forming said n^(−th) layeronto at least one of said n+1^(−th) layer of said mold and said signalsubstrate; a step of rotating said mold and said signal substrate, withsaid mold and said signal substrate superposed one atop of the other insuch a manner that said n+1^(th) layer is positioned on the inner side,so as to stretch said radiation curable material for adhesion; and astep of emitting radiation and accordingly hardening said radiationcurable material. Using such a manufacturing method above, it ispossible to prevent entry of air bubbles without reducing the pressuresince air bubbles inside the n^(−th) layer are loosed during stretching.

The 21^(st) aspect of the present invention is the method ofmanufacturing a multi-layer optical information recording medium of the12^(th) aspect, wherein said n+1^(−th) layer is of a radiation curablematerial, and said step (a) comprises: a step of dripping a radiationcurable material for transfer which is for forming said n+1^(−th) layeronto at least one of said mold and said n^(−th) layer on said signalsubstrate; a step of rotating said mold and said signal substrate, withsaid mold and said signal substrate superposed one atop of the other insuch a manner that said n^(−th) layer is positioned on the inner side,so as to stretch said radiation curable material for transfer; and astep of emitting radiation and accordingly hardening said radiationcurable material.

The 22^(nd) aspect of the present invention is an apparatus formanufacturing a multi-layer optical information recording medium onwhose one surface recording and reproduction are performed and whichcomprises an isolation layer between a plurality of signal recordinglayers, comprising:

n+1^(−th) layer forming means which, at the time of forming saidisolation layer on said signal recording layers, forms an n+1^(−th)layer on a surface of a mold in which there is a signal recording areawhich contains at least one of a guide groove and a pit, whilecontrolling a thickness distribution along the radius direction of saidmold;

bonding means which forms an n^(−th) layer, whose thickness distributionis controlled along the radius direction, between said n+1^(−th) layerwhich is on said mold and a signal substrate which comprises said signalrecording layers, and bonds said n+1^(−th) layer which is on said moldwith said signal substrate; and

peeling means which peels off said mold from said n+1^(−th) layer andaccordingly obtains said isolation layer which comprises said n+1^(−th)layer, whose surface seats a signal on said mold which has beentransferred, and said n^(−th) layer. Using such an apparatus formanufacturing a multi-layer optical information recording mediumdescribed above, it is possible to control the thickness distribution ofthe isolation layer which comprises both the n+1^(−th) layer and then^(−th) layer and makes the thickness distribution uniform since thethickness distributions along the radius direction of the n+1^(−th)layer and the n^(−th) layer are controlled, and therefore, animprovement in mass productivity attributed to a better yield isexpected. Further, it is possible to stably record in and reproduce fromthe signal recording layers which are disposed on the both sides of theisolation layer, and hence, to obtain an excellent signal.

The 23^(rd) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the22^(nd) aspect, wherein in the event that said n+1^(−th) layer is of aradiation curable material, said n+1^(−th) layer forming meanscomprises:

dripping means which drips said radiation curable material onto an innerround portion of said mold;

rotating means which rotates said mold to which said radiation curablematerial has been dripped; and

hardening means which emits radiation and accordingly hardens saidradiation curable material. Such a structure described above makes itpossible to easily form the n+1^(−th) layer.

The 24^(th) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the23^(rd) aspect, wherein said mold is rotated while dripping saidradiation curable material onto said inner round portion of said mold.

The 25^(th) aspect of the present invention is the apparatus formanufacturing a multi layer optical information recording medium of the23^(rd) aspect or the 24^(th) aspect, wherein before dripping saidradiation curable material onto said inner round portion of said mold,in the event that there is a center hole approximately at the center ofsaid mold, said center hole is capped with a lid and said radiationcurable material is then dripped from above said lid. Such a structuredescribed above makes it possible to easily control the thicknessdistribution along the radius direction of the n+1^(−th) layer.

The 26^(th) aspect of the present invention is he apparatus formanufacturing a multi-layer optical information recording medium of the22^(nd) aspect, wherein in the event that said n^(−th) layer is of aradiation curable material, said bonding means comprises:

dripping means which drips said radiation curable material onto an innerround portion within said n+1^(−th) layer of said mold or an inner roundportion of said signal substrate;

rotating means which rotates said mold or said signal substrate to whichsaid radiation curable material has been dripped;

superposing means which superposes said mold and said signal substrateone atop of the other after the rotations in such a manner that thesurface coated with said radiation curable material is directed towardthe inner side; and

hardening means which emits radiation and accordingly hardens saidradiation curable material. Such a structure described above makes itpossible to easily bond the mold seating the n+1^(−th) layer with thesignal substrate.

The 27^(th) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the26^(th) aspect, wherein the rotations are effected while dripping saidradiation curable material onto said inner round portion of said mold orsaid inner round portion of said signal substrate.

The 28^(th) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the26^(th) aspect or the 27^(th) aspect, wherein before dripping saidradiation curable material, in the event that there is a center holeapproximately at the center of said mold or said signal substrate, saidcenter hole is capped with a lid and said radiation curable material isthen dripped from above said lid. Such a structure described above makesit possible to easily control the thickness distribution along theradius direction of the n^(−th) layer.

The 29^(th) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the26^(th) aspect, wherein said superposing means contains depressurizingmeans, and superposes said mold and said signal substrate one atop theother after reducing an ambient pressure with said depressurizing means.Such a structure described above prevents air bubbles from getting mixedinto the isolation layer, and an improvement in yield is expected.

The 30^(th) aspect of the present invention is the apparatus formanufacturing a multi-layer optical information recording medium of the22^(nd) aspect, wherein in the event that said n^(−th) layer is of aradiation curable material, said bonding means comprises:

dripping means which drips a radiation curable material for adhesionwhich is for forming said n^(−th) layer onto at least one of saidn+1^(−th) layer which is on said mold and said signal substrate;

stretching means which superposes said mold and said signal substrateone atop the other in such a manner that said n+1^(−th) layer ispositioned on the inner side, rotates said mold and said signalsubstrate and stretches said radiation curable material for adhesion;and

hardening means which emits radiation and accordingly hardens saidradiation curable material. Such a structure described above looses airbubbles inside the n^(−th) layer without reducing the pressure duringstretching and prevents entry of air bubbles, and therefore, animprovement in yield is expected.

The 31^(st) aspect of the present invention is a multi-layer opticalinformation recording medium, comprising:

a substrate layer which is capable of holding signal information;

an n^(−th) layer which is formed above said substrate layer;

an n+1^(−th) layer which is formed above said n^(−th) layer; and

a protection layer which is formed above said n+1^(−th) layer,

wherein the thickness as it is with said n^(−th) layer and saidn+1^(−th) layer superposed one atop the other is uniform.

The 32^(nd) aspect of the present invention is the multi-layer opticalinformation recording medium of the 31^(st) aspect, wherein thethickness of said n+1^(−th) layer along the radius direction and thethickness of said n^(−th) layer along the radius direction arereciprocal from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram which shows the method of manufacturing amulti-layer optical information recording medium according to oneembodiment of the present invention.

FIG. 2 is a drawing which shows one example of the method of applyingthe transfer layer at the transfer layer forming step according to oneembodiment of the present invention.

FIG. 3 is a drawing which shows one example of the method of hardeningthe transfer layer at the transfer layer forming step according to oneembodiment of the present invention.

FIG. 4 is a drawing which shows one example of the adhesive layerforming step according to one embodiment of the present invention.

FIG. 5 is a drawing which shows the thickness distributions of theadhesive layer and the isolation layer which are obtained as a result ofthe steps which are shown in FIGS. 2, 3 and 4.

FIG. 6 is a drawing which shows one example of the peeling step ofpeeling off the mold according to one embodiment of the presentinvention.

FIG. 7 is a drawing which shows the second example of the adhesive layerforming step according to one embodiment of the present invention.

FIG. 8 is a drawing which shows the method of forming the transfer layerand the adhesive layer which have different thickness distributions fromthose shown in FIGS. 2 through 7.

FIG. 9 is a drawing which shows the thickness distributions which areobtained by the forming method which is shown in FIG. 8.

FIG. 10 is a drawing which shows the adhesive layer forming step as itis when a pressure-sensitive adhesive is used as the adhesive layeraccording to one embodiment of the present invention.

FIG. 11 is a drawing which shows the transfer layer forming step as itis when a pressure-sensitive adhesive is used as the transfer layeraccording to one embodiment of the present invention.

FIG. 12 is a drawing which partially shows a conventional method ofmanufacturing a multi-layer optical information recording medium.

FIG. 13 is a cross sectional view of a multi-layer optical informationrecording medium which is manufactured by the conventional technique.

FIG. 14 is a cross sectional view of a multi-layer optical informationrecording medium which is manufactured by the manufacturing methodaccording to the present invention.

FIG. 15 is a drawing which shows the modified embodiment of the presentinvention.

DESCRIPTION OF SYMBOLS

-   100 mold-   101, 108, 1006, 1106 center hole-   102 concave/convex portion-   103 transfer layer-   105 signal substrate-   106 signal recording film-   107, 706, 804 adhesive layer-   109 transferred concave/convex portion-   110 isolation layer-   200, 403, 802 UV curable resin-   201, 401, 701 rotation table-   202 lid-   205, 400 nozzle-   210 UV lamp-   402, 703, 1001 center pin-   404 ring-shaped UV curable resin-   405 stretched adhesive layer-   600 fixing stage-   601 center post-   602 nozzle-   610 wedge-   615 compressed air-   620 pre-peeling intermediate article-   702 table-   704 vacuum pump-   705 depressurizing chamber-   801 stretched transfer layer-   803 hardened transfer layer-   1000 fix table-   1005, 1105 pressure-sensitive adhesive-   1010 roller-   1100 balloon-   1101 air

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will now be described indetail with reference to the associated drawings.

Embodiment 1

An embodiment 1 will now be described with reference to FIG. 1. This isan example that there is a tendency that a thickness distribution alongthe radius direction of a transfer layer, which is one example of then+1^(−th) layer according to the present invention, is thick in an innerround portion of a mold but is gradually thinner toward outer rounds andthat a thickness distribution along the radius direction of an adhesivelayer, which is one example of the n^(−th) layer according to thepresent invention, is thin in an inner round portion of a signalsubstrate but is gradually thicker toward outer rounds.

FIG. 1 is a conceptual diagram of the present invention. First, as shownin FIG. 1( a), a transfer layer 103 is formed on concave/convex portions102 in a surface of a mold 100 which is circular. The concave/convexportions 102 formed within a signal recording area comprise at least oneof a guide groove and a pit. An example may be a groove whose trackpitch is 0.32 micron and depth is 20 nm and which comprises a wobblewhich is indicative of address information. Further, there may be acenter hole 101 at the center of the mold 100. The transfer layer 103 isformed so as to have a thickness distribution along the radius directionthat the layer is thick in an inner round portion of the mold but isgradually thinner toward an outer round portion of the mold.

Next, as shown in FIG. 1( b), a signal recording film 106, which is oneexample of the signal recording layer according to the presentinvention, is disposed on a surface of the signal substrate 105. Anadhesive layer 107 is formed between the surface of the signal substrate105 which seats the signal recording film 106 and the mold 100 whichseats the transfer layer 103, thereby bonding the mold 100 and thesignal substrate 105. The signal substrate 105 may comprise a centerhole 108. The adhesive layer 107 is formed so as to have a thicknessdistribution along the radius direction that the layer is thin in aninner round portion but is gradually thicker toward an outer roundportion. Since the thickness distributions of the transfer layer 103 andthe adhesive layer 107 are opposite to each other, an isolation layer110 which comprises these two layers has a uniform thicknessdistribution. At last, as shown in FIG. 1( c) , the mold 100 is peeledoff from the interface with the transfer layer 103. On a surface of thetransfer layer 103, concave/convex portions 109 transferred from themold 100 are formed. While the transfer layer 103 is a layer fortransfer of the concave/convex portions 102 on the mold 100, it isnecessary to appropriately choose the respective materials so that thepeeling at the interface between the transfer layer 103 and the mold 100will be easy.

In the manner described above, the isolation layer 110 whose thicknessdistribution is uniform along the radius direction is obtained. On thetransferred concave/convex portions 109 of the isolation layer 110, afurther isolation layer or a protection layer 3000 is formed afterforming a signal recording film 3001. This is the outline of the presentinvention. The signal substrate 105 may comprise other signal recordinglayer (not shown) below the signal recording film 106. In other words,the signal recording film 106 may be formed on the isolation layer.

The steps shown in FIGS. 1( a) through (c) will now be described indetail.

First, a step of forming the transfer layer will be described inrelation to one example. FIGS. 2 and 3 show an example that the transferlayer is formed through spin coating, using an UV curable resin, whichis one example of the radiation curable material according to thepresent invention, as the material of the transfer layer. The mold 100comprising the center hole 101 as that shown in FIG. 2( a) is prepared.The diameter of the center hole 101 is 15 mm, and the outer diameter ofthe mold 100 is 120 mm. Since an UV curable resin is used as thematerial of the transfer layer, it is preferable that the material ofthe mold is plastic which is transparent to UV light to a certain extentsuch as an acrylic resin, an olefine resin, polycarbonate and anorbornene-based resin.

Next, as shown in FIG. 2( b), the mold 100 is placed on a rotation table201. The rotation table 201 fixes the mold 100 by vacuum suction orotherwise appropriate method. The center hole 101 is covered with a lid202. While the lid 202 may have outer dimensions with a diameter of 15mm through 42 mm, the diameter is 22 mm in this example. A nozzle 205 ispositioned above the lid 202, and dripping of an UV curable resin 200which is the material of the transfer layer is started. The rotationtable 201 may start rotating before the dripping. The viscosity of theUV curable resin 200 is 150 mPa·s. For the UV curable resin 200, it isnecessary to select such a material which is easily peeled off from theinterface with the mold 100 as shown in FIG. 1( c) . An example is anacrylic material which causes radical polymerization under irradiationof UV light. The resin dripping time is 9 sec. Approximately at the sametime as the dripping, the rotation table 201 starts rotating as shown inFIG. 2( c). The initial 6 sec is a low speed but the subsequent numberof revolutions is 2000 rpm, and the rotation time at 2000 rpm is 10 sec.Hence, rotations continue for 7 sec after the dripping ends. Therotation table 201 stops rotating after the rotations.

Steps following the stop are shown in FIG. 3. FIG. 3( a) shows a stateimmediately after the stop. The tendency is that the layer is thick inan inner round portion of the mold but is gradually thinner toward anouter round portion of the mold. FIG. 3( b) shows the thickness of thetransfer layer along the radius direction. The layer is as thick asabout 15 microns in the vicinity of the radius of 20 mm but is graduallythinner along the radius direction with a distance from the center andbecomes about 13 microns over 58 mm from the center in the radiusdirection. Such a thickness distribution can be controlled based on thedripping time for dripping the UV curable resin, the number ofrevolutions of the rotation table during the dripping and the rotationtime after the termination of the dripping. As the number of revolutionsand the rotation time increase, the thickness distribution along theradius direction changes less and becomes generally uniform.

At last, as shown in FIG. 3( c), with the lid 202 removed from above themold 100, the UV curable resin 200 is hardened using an UV lamp 210,thereby obtaining the transfer layer 103. The purpose of removing thelid 202 prior to the hardening is to prevent the UV curable resin 200from becoming solid after the hardening so that the lid 202 gets removedeasily. The lid 202 may be grabbed at with a robot arm for removal, ormay be partially formed by a magnetic material and lifted up using amagnet. Although the hardening occurs on the rotation table 201 in FIG.3( c), the mold 100 may be moved over to a different table which isequipped with an UV lamp for hardening. The UV lamp 210 may be a metalhalide lamp, a mercury lamp, a xenon lamp, etc.

A step of forming the adhesive layer will now be described in relationto one example. This example uses an UV curable resin as the adhesivelayer. As the UV curable resin, it is necessary to choose a materialwhich strongly adheres to the material of the signal substrate, thematerial of the signal recording layers, and further, to the transferlayer 103. An example is an acrylic material. FIG. 4 shows stretching ofthe adhesive layer through spinning. As shown in FIG. 4( a), the signalsubstrate 105 which seats the signal recording film 106 is placed andfixed on a rotation table 401. The signal substrate 105 has outerdimensions with a diameter of 120 mm, the diameter of the center hole108 is 15 mm, and the material of the signal substrate 105 ispolycarbonate, plastic of acryl or olefin, etc. The signal recordingfilm 106 may be a phase-conversion film of GeSbTe, AgInSbTe or the like,a recording film such as a magnetic film or a pigment film, dielectricfilms of ZnS or the like which sandwich these films, and a metalreflection film, etc. Sputtering, vapor deposition or the like isgenerally used for film deposition.

Fixing on the rotation table 401 is realized by means of vacuum suctionof a contact surface with the signal substrate 105. A center pin 402which fits in the center hole 108 is disposed to the rotation table 401,which allows centering of the signal substrate 105. With the rotationtable 401 rotating, an UV curable resin 403 is dripped out from a nozzle400 which is disposed at the radius of 20 through 30 mm on the signalsubstrate 105. An acrylic resin whose viscosity is 450 mPa·s is used asthe UV curable resin 403 in this example. Since the signal substrate 105is rotated, the UV curable resin 403 becomes ring-shaped.

The mold 100 obtained through the steps shown in FIGS. 2 and 3 is thensuperposed on the signal substrate 105. As shown in FIG. 4( b), there isthe ring-shaped UV curable resin 404 on the signal substrate 105, themold 100 is placed on this from above in such a manner that the transferlayer 103 contacts the ring-shaped UV curable resin 404. The center hole101 of the mold 100, having the diameter of 15 mm, fits with the centerpin 402, which aligns the center of the signal substrate 105 with thecenter of the mold 100. The superposition may be carried out under areduced pressure, for the purpose of avoiding air bubbles which may getmixed in when the transfer layer 103 contacts the ring-shaped UV curableresin 404.

The rotation table 401 then rotates at a high speed as shown in FIG. 4(c), whereby the UV curable resin stretches all over the surface. In thisexample, the rotation table 401 then rotates at a high speed of 5000 rpmfor 30 sec. As a result, thus stretched adhesive layer 405 is formedbetween the transfer layer 103 and the signal substrate 105. For stablepeeling at a peeling step which follows this, it is necessary that theadhesive layer 405 stretched as shown in FIG. 4( c) is not in a directcontact with the mold 100. After the stretching, thus stretched adhesivelayer 405 is hardened from the mold 100 side using an UV lamp in asimilar fashion to that shown in FIG. 3( c). Since the mold 100 istransparent, hardening is possible.

FIG. 5 shows a thickness distribution of thus obtained adhesive layerand a thickness distribution of the isolation layer which is comprisedof the transfer layer and the adhesive layer. As shown in FIG. 5( a),the thickness distribution of the adhesive layer is that the layer is 10microns in an inner round portion of the layer but is gradually thickertoward an outer round portion of the layer and becomes 12.5 microns atan outer circumferential edge, owing to centrifugal force resulting fromthe high-speed rotations. Meanwhile, the thickness distribution of theisolation layer which is comprised of the transfer layer and theadhesive layer is as shown in FIG. 5( b). The thickness distribution,which is a combination of FIG. 3( b) and FIG. 5( a), is that the layeris within a range of 24.5±0.5 microns from the inner rounds through theouter rounds and thus considerably uniform.

At last, FIG. 6 shows the peeling step of peeling off the mold. Theillustrated peeling method uses a wedge and compressed air. As FIG. 6(a) shows, a pre-peeling intermediate article 620, which is the mold 100and the signal substrate 105 as they are bonded to each other, obtainedat the bonding step is fixed on a fixing stage 600. Vacuum suction is apreferable fixing method. A center post 610 is disposed to the fixingstage 600, and a nozzle 602 is formed in a part of the center post 610.

A wedge 610 is then pushed out from the center post 601 as shown in FIG.6( b) and inserted to the interface between the mold 100 and thetransfer layer 103. At this stage, the transfer layer 103 may bedisplaced to a certain extent because of the wedge 610. After the wedge610 is inserted, compressed air 615 is gushed out through the nozzle602. The compressed air 615 enters the interface between the mold 100and the transfer layer 103 to which the wedge 610 has been inserted, andstarts peeling off the mold 100. After a while, the mold 100 is finelypeeled off from the interface with the transfer layer 103 as shown inFIG. 6( c), thereby exposing the concave/convex portions 109 transferredto the surface of the isolation layer 110 (the surface of the transferlayer 103). In FIG. 6( b), in the event that the peeling does notprogress with the compressed air 615 alone, the mold 100 may be liftedup from above, and the peeling will proceed more efficiently.

In order to complete the post-peeling signal substrate as a multi-layeroptical information recording medium, it is necessary to form the signalrecording layers further on thus transferred concave/convex portions 109through sputtering and uniformly form a transparent cover layer (whosethickness is 75 microns for instance) further on this, after the peelingstep shown in FIG. 6. A method of forming the transparent cover layermay be a method which requires to bond, with a transparent adhesive, atransparent film whose thickness accuracy is high and whose thickness isthinner than that of the desired transparent cover layer, oralternatively, a method which requires to directly form a layer having adesired thickness level using a transparent overcoat agent. In amulti-layer optical information recording medium fabricated by themethod described in relation to this embodiment, since the isolationlayer which isolates the signal recording layers from each other isuniform, a stray light or the like from the signal recording layer whichis adjacent to the signal recording layer in which recording orreproduction is being executed exerts a constant level of influence atany radius, which in turn makes it possible to stably record orreproduce and obtain an excellent and stable signal at any radius.

While this embodiment uses UV curable resins for both the transfer layerand the adhesive layer, a thermosetting material may be used instead, inwhich case it is necessary to choose metals such as nickel and iron, orhighly heat-resisting plastics such as an ABS resin as the material ofthe mold.

In addition, although the mold 100 is superposed from above the signalsubstrate 105 in FIG. 4, the mold 100 may be placed below and the signalsubstrate 105 may be superposed from above. Further, although the UVcurable resin for adhesion 403 is dripped upon the signal substrate 105,the UV curable resin for adhesion 403 may be dripped upon the transferlayer 103 which is on the mold 100. Any one of the signal substrate 105and the mold 100 may be placed on the other. In addition, the UV curableresin for adhesion 403 may be dripped upon both the signal substrate 105and the mold 100. In either case, a rotating condition may be determinedconsidering the wettability of the UV curable resin for adhesion and thesurface subjected to the drops and the like, so as to obtain a desiredthickness distribution for the adhesive layer.

Embodiment 2

In relation to the embodiment 2, a second adhesive layer forming stepwill be described which is different from the method of forming theadhesive layer shown in FIG. 4. FIG. 7 is a conceptual diagram. As shownin FIG. 7( a), the signal substrate 105 is held to a rotation table 701and the ring-shaped UV curable resin 404 is disposed in a similarfashion to that shown in FIG. 4( a). However, the dripping position isat the radius of 15 mm, which is toward the inner side as compared tothe embodiment 1. The UV curable resin for adhesion may be the same asthat used in the embodiment 1.

The rotation table 701 is then rotated at a high speed as shown in FIG.7( b). As a result, the stretched adhesive layer 405 is formed on thesignal substrate 105. A rotating condition is 5000 rpm for 20 sec. Underthis condition, a thickness distribution which is approximately the sameas that shown in FIG. 5( a) is obtainable. The mold 100 now seating thetransfer layer 103 obtained as shown in FIG. 3( c) and the signalsubstrate 105 now seating an adhesive layer 706 are then loaded into adepressurizing chamber 705 and superposed one atop the other under areduced pressure as shown in FIG. 7( c). They are superposed in such amanner that the transfer layer 103 and the adhesive layer 706 contactwith each other. There is a table 702 for fixing the signal substrate105 within the depressurizing chamber 705. A center pin 703 is disposedto the table 702, which allows to align the mold 100 which is placedfrom above and the fixed signal substrate 105 at the center.

After the loading of the signal substrate 105 and the mold 100, thedepressurizing chamber 705 is depressurized by means of a vacuum pump704. Since the superposition is carried out under a reduced pressure,air bubbles will not get mixed in between the transfer layer 103 and theadhesive layer 706. The depressurizing chamber 705 is opened toatmosphere and air is introduced after the superposition, the signalsubstrate 105 and the mold 100 are unloaded, and the adhesive layer 706is hardened using the UV lamp 210 as shown in FIG. 3( c). After thehardening, the mold 100 is peeled off by the method shown in FIG. 6.Steps after the peeling are similar to those described in relation tothe embodiment 1 and therefore will not be described again.

Although the embodiment 2 requires to form the adhesive layer 706 on thesignal substrate 105 and the mold 100 is superposed, the adhesive layer706 may be formed on the transfer layer 103 and placed on the signalsubstrate 105 which does not comprise an adhesive layer. Alternatively,adhesive layers may be disposed to both the signal substrate 105 and themold 100 and the two may be superposed one atop the other. In eithercase, a rotating condition may be determined considering the wettabilityof the UV curable resin for adhesion and the surface subjected to thedrops and the like, so as to obtain a desired thickness distribution forthe adhesive layer.

In addition, after the step shown in FIG. 7( c), the signal substrate105 and the mold 100 superposed one atop the other may be unloaded fromthe depressurizing chamber 705 and loaded into a pressurizing chamber,to thereby burst very small air bubbles (which contain depressurized airinside) by means of autoclave.

Embodiment 3

In relation to the embodiment 3, an example will be described in whichthere is a tendency is that the thickness distribution along the radiusdirection of the transfer layer is that the layer is thin in the innerround portion of the mold but is gradually thicker toward the outerrounds and the thickness distribution along the radius direction of theadhesive layer is that the layer is thick in the inner round portion ofthe signal substrate but is gradually thinner toward the outer rounds.The transfer layer is formed as shown in FIGS. 7( a) and (b), and theadhesive layer is formed by a method which is approximately the same asthat shown in FIGS. 2 and 3. First, the outline of the steps will bedescribed with reference to FIG. 8.

First, the transfer layer is formed. As shown in FIG. 8( a), an UVcurable resin for transfer is dripped upon the mold 100 which is fixedto the rotation table 701, the rotation table 701 rotates, and the UVcurable resin stretches. The mold 100 may be the same as that used inthe embodiments 1 and 2. The UV curable resin may be the same as thatused in the embodiments 1 and 2. The dripping position is at the radiusof 11 mm. The rotations are at 4000 rpm, and the rotation time is 5 sec.The transfer layer 801 thus stretched is hardened using an UV lamp,after the end of the rotations. FIG. 9( a) shows a thicknessdistribution of thus stretched transfer layer 801. The layer tends tobecome gradually thicker, starting at 8 microns in the inner roundportion and reaching 10 microns in the outer round portion.

This is followed by bonding with the signal substrate. As shown in FIG.8( b), the signal substrate 105 which seats the signal recording film106 is fixed on the rotation table 201 by a method similar to thatdescribed with reference to FIGS. 2 and 3, the center hole 108 iscovered with the lid 202 whose diameter is 22 mm, and an UV curableresin for adhesion 802 is applied from the nozzle 205. The rotationtable 201 is rotated while dripping the UV curable resin 802. At thisstage, the signal substrate 105 may be similar to that used in theembodiments 1 and 2. The UV curable resin 802 is of an acrylic resinexhibiting 200 mPa·s, unlike in the embodiment 1. The resin drippingtime is 9 sec. The initial 6 sec is a low speed, the subsequent numberof revolutions is 2000 rpm, and the rotation time is 10 sec. The lid 202is removed after the end of the rotations. A thickness distribution ofthe resulting adhesive layer 804 is as shown in FIG. 9( b). The layer is17 microns in the inner round portion and 15 through 16 microns in theouter round portion. This means that the rotating condition iscontrolled so that the layer will become gradually thinner through theouter rounds.

At last, the signal substrate 105 and the mold which seats thus hardenedtransfer layer 803 are loaded into a depressurizing chamber as thatshown in FIG. 8( c) and superposed one atop the other under a reducedpressure, without hardening the UV curable resin 802. The depressurizingchamber 705 is depressurized by means of the vacuum pump 704. The centerpin 703 of the table 702 aligns the signal substrate 105 and the mold100 at the center. The signal substrate 105 and the mold 100 now placedone atop the other are irradiated with UV light, thereby hardening theadhesive layer 804. The mold 100 is peeled off by the method shown inFIG. 6, after the hardening. FIG. 9( c) shows a thickness distributionof the resulting isolation layer (which is comprised of the transferlayer and the adhesive layer). Since the thickness distributions alongthe radius direction of the transfer layer 103 and the adhesive layer804 are each controlled, the thickness distribution of the isolationlayer is within a range of 25.5±0.5 microns and thus considerablyuniform.

Steps after the peeling are similar to those described in relation tothe embodiment 1 and therefore will not be described again.

While the embodiment 3 requires to form the adhesive layer 804 on thesignal substrate 105 for stable fabrication, the adhesive layer 804 maybe formed on the hardened transfer layer 803 which is on the mold 100and placed on a signal substrate which does not comprise an adhesivelayer. Alternatively, the adhesive layer 804 may be formed on the signalsubstrate 105 and hardened with the lid 202 removed, and superposedwithin the depressurizing chamber 705 without hardening the stretchedtransfer layer 801 which is shown in FIG. 8( a).

This demands to harden the transfer layer 801 which was stretched bymeans of UV light after superposition, and it therefore is essentialthat the UV curable resin for transfer exhibits sufficiently strongadhesion with the hardened adhesive layer. Otherwise, peeling at theinterface between the mold 100 and the transfer layer will not work wellat the peeling step. In either case, it is important to determine arotating condition so as to obtain a desired thickness distribution forthe transfer layer or the adhesive layer to which the UV curable resinfor transfer is to be applied.

In addition, after the step shown in FIG. 8( c), the signal substrate105 and the mold 100 superposed one atop the other may be unloaded fromthe depressurizing chamber 705 and loaded into a pressurizing chamber,to thereby collapse very small air bubbles (which contain depressurizedair inside) by means of autoclave.

Embodiment 4

In relation to the embodiment 4, examples will be described in which thetransfer layer or the adhesive layer is of a pressure-sensitiveadhesive.

The first example is that the transfer layer is of an UV curable resinas in the embodiments 1 through 3 described above while the adhesivelayer is of a pressure-sensitive adhesive. The transfer layer is formedin a similar fashion to that shown in FIG. 8( a) which shows theembodiment 3. The method shown in FIG. 8( a) does not use a lid unlikethe methods shown in FIGS. 2 and 3, and therefore, is easy to implement.When the same UV curable resin for transfer as that used in theembodiment 3 is used, a thickness distribution becomes as shown in FIG.9( a). A method of forming the transfer layer is similar to thatdescribed above and therefore will not be described again. When apressure-sensitive adhesive is used as the adhesive layer, it isnecessary that the pressure-sensitive adhesive is prepared in the shapeof a disk in advance.

It is necessary to control a thickness distribution of thepressure-sensitive adhesive to that shown in FIG. 9( b). Since apressure-sensitive adhesive is half solid, it is generally easy tocontrol the thickness distribution. FIG. 10 shows methods of fabricatingthe isolation layer where a pressure-sensitive adhesive is used as theadhesive layer. FIG. 10( a) shows a method which requires to bond apressure-sensitive adhesive 1005 to the signal substrate 105. Thepressure-sensitive adhesive 1005 comprises a center hole 1006 andexhibits such a thickness distribution that the adhesive is graduallythinner from inner rounds toward outer rounds. Because of the centerhole 1006, it is possible to align to the center of the signal substrate105, using a center pin 1001 of a fix table 1000. By means of a roller1010, the pressure-sensitive adhesive 1005 is bonded starting at anouter circumferential edge of the signal substrate 105 through the otherouter circumferential edge. The roller 1010 is preferably ofsurface-treated rubber (through fluorination for instance), so that theroller 1010 will not stick to the pressure-sensitive adhesive 1005. Whenthe roller 1010 is made of rubber, even in atmosphere, it is hard forair bubbles to enter between the pressure-sensitive adhesive 1005 andthe signal substrate 105 owing to the elasticity of the rubber.

The step shown in FIG. 10( a) may be executed within the depressurizingchamber. When the pressure which pushes the roller 1010 against thepressure-sensitive adhesive 1005 is sufficiently high, it is possible tofill the concave/convex portions on the signal substrate with thepressure-sensitive adhesive 1005. Further, a protection film whichprevents sticking to the roller 1010 may be disposed on a surface of thepressure-sensitive adhesive 1005 contacting the roller 1010. FIG. 10( b)shows superposition of the mold 100 now seating the hardened transferlayer 803 within the depressurizing chamber 705. The sequence is thesame as that described in relation to the embodiments 2 and 3. It isneedless to mention that where there is a protection film disposed tothe pressure-sensitive adhesive 1005, it is necessary to peel off theprotection film prior to this step. In the event that thepressure-sensitive adhesive 1005 has such a characteristic as anUV-hardening characteristic and therefore can harden, thepressure-sensitive adhesive 1005 may be hardened after thesuperposition. At last the peeling step is executed, thereby obtainingthe isolation layer which exhibits a uniform thickness distribution.

The second example is that the transfer layer is of a pressure-sensitiveadhesive which hardens to UV light while the adhesive layer is of an UVcurable resin. The adhesive layer is the same as that shown in FIGS. 7(a) and (b) and therefore will not be described again. FIG. 11 shows amethod of superposing a pressure-sensitive adhesive for transfer 1105 onthe mold 100 using a balloon 1100. The pressure-sensitive adhesive 1105is formed so as to exhibit a thickness distribution that the adhesive isgradually thinner from inner rounds through outer rounds. As FIG. 11(a), the. pressure-sensitive adhesive 1105 comprises a center hole 1106,and is registered to the center of the mold 100 by means of the centerpin 1001 of the fix table 1000. The balloon 1100 is moved down fromabove the center of the fix table 1000, and air 1101 is graduallyintroduced. The balloon 1100 is preferably of surface-treated rubber(through fluorination for instance), so that the balloon 1100 will notstick to the pressure-sensitive adhesive 1105.

As the air 1101 enters the balloon 1100, the balloon 1100 which iselastic swallows up as shown in FIG. 11( b), thereby causing thepressure-sensitive adhesive 1105 to contact the mold 100 starting at thecenter of the mold 100 toward the outer circumferential edge of the mold100. The elasticity of the balloon 1100 and the gradual contact of thepressure-sensitive adhesive 1105 with the mold 100 prevent air bubblesfrom entering into the interface between the pressure-sensitive adhesive1105 and the mold 100. In addition, the pressure-sensitive adhesive 1105is pushed by the balloon 1100 and hence the concave/convex portions 102on the mold 100 is filled with the pressure sensitive adhesive 1105.After this step, UV light is irradiated and the pressure-sensitiveadhesive 1105 is accordingly hardened. The hardening prevents theconcave/convex portions 102 formed in the pressure-sensitive adhesive1105 from getting deformed even at the peeling step. The hardening ofthe pressure-sensitive adhesive is followed by superposition of thesignal substrate and hardening of the adhesive layer by a similar methodto that shown in FIG. 7( c), and at last, the peeling step is executed.

While the foregoing has described the embodiment 4 in relation to anexample that a roller is used for the method of forming the adhesivelayer and a balloon is used for the method of forming the transferlayer, a balloon may be used for the method of forming the adhesivelayer and a roller may be used for the method of forming the transferlayer.

Further, the embodiment 4 relates to an example that the transfer layeror the adhesive layer is of a pressure-sensitive adhesive, both thetransfer layer and the adhesive layer may be of a pressure-sensitiveadhesive. In addition, the thickness distribution of the UV curableresin described above may be controlled such that the resin is graduallythinner from inner rounds through outer rounds, to thereby control thethickness distribution of the pressure-sensitive adhesive such that theadhesive becomes gradually thicker from inner rounds through outerrounds.

With the method of and the apparatus for manufacturing a multi-layeroptical information recording medium described above, it is possible tocontrol the thickness distribution of the isolation layer whichcomprises the transfer layer and the adhesive layer, and hence, make thethickness of the isolation layer uniform. This permits to stably recordin and reproduce from the signal recording layers which are disposed onthe both sides of the isolation layer, and hence, to obtain an excellentsignal. Further, it is possible to provide a production margin for avariation in thickness of the isolation layer, and therefore, improvethe mass productivity.

FIG. 14 shows one example of a multi-layer optical information recordingmedium 3002 which is manufactured in this manner. Across section of themulti-layer optical information recording medium 3002 which ismanufactured by the manufacturing method according to the embodiments ofthe present invention shows that the interface between the transferlayer 103 and the adhesive layer 107 which form the isolation layer 110is inclined from the center toward the outer side and. that theisolation layer 110 has a constant level of thickness along the radiusdirection. In this case, the extent of the inclination varies dependingon a manufacturing condition. It is possible that the interface willbecome substantially horizontal in some cases.

Further, in the description above, with respect to the thicknessdistributions along the radius direction of the transfer layer and theadhesive layer, the both thickness distributions may be controlled suchthat the two complements with each other or the thickness distributionof one of the layers may be controlled considering the thicknessdistribution of the other one of the layers, in which case if the totalthickness of the transfer layer and the adhesive layer is uniform alongthe radius direction, an effect similar to that described above isobtained. Still further, the thickness distributions along the radiusdirection of the transfer layer and the adhesive layer may each beuniform.

In addition, although the foregoing has described that the isolationlayer is formed by two layers of the transfer layer and the adhesivelayer, the isolation layer may be formed by a plurality of layers whichmay be three or more. When the isolation layer is formed by three layersfor instance, the signal substrate according to the present inventioncorresponds to the signal substrate 105 and the n−1^(−th) layer which isformed on the signal substrate 105. In the event that the isolationlayer is formed by m layers, the signal substrate according to thepresent invention corresponds to the signal substrate 105 and a layerwhich is lamination of the first through the n−1^(−th) layer. FIG. 15shows an example of such a signal substrate.

The configuration that the n+1^(−th) layer and the n^(−th) layer areformed and the thickness distribution of one of the layers is controlledconsidering the thickness distribution of the other layer includes aconfiguration that the thickness distribution of the one layer iscontrolled considering a thickness distribution which is observed on animmediately precedent production batch. In this case, the thicknessdistribution of one of the layers may be controlled while considering athickness distribution of a prototype which may be the very firstproduction batch.

While the embodiments 1 through 4 are on an example that there is onlyone isolation layer, the present invention is not limited to this. Theremay be a plurality of isolation layers, in which case the presentinvention is applied to at least one of the plurality of isolationlayers.

In addition, as in the embodiments 2 and 3, after FIG. 10( b), thesignal substrate 105 and the mold 100 superposed one atop the other maybe unloaded from the depressurizing chamber 705 and loaded into apressurizing chamber, to thereby collapse very small air bubbles (whichcontain depressurized air inside) by means of autoclave.

While the foregoing has described the embodiments 1 through 4 inrelation mainly to the method of manufacturing a multi-layer opticalinformation recording medium according to the present invention, therespective means which form the apparatus for manufacturing amulti-layer optical information recording medium according to thepresent invention are the rotation table, the nozzle and the like whichare used at the respective steps shown in FIGS. 2 through 4, 6 through8, 10 and 11.

Further, although the foregoing has described that the signal recordinglayers according to the present invention is the signal recording film106, the signal recording layers according to the present invention maybe formed by guide grooves or pits.

Still further, although the foregoing has described that the radiationcurable material according to the present invention is an UV curableresin, the radiation curable material according to the present inventionmay be any other material which hardens to radiation.

As described above, the method of and the apparatus for manufacturing amulti-layer optical information recording medium according to thepresent invention allow to stably record in and reproduce from thesignal recording layers which are disposed on the both sides of theisolation layer, and hence, to obtain an excellent signal.

1. A multi-layer optical information recording medium, comprising: asubstrate layer which is capable of holding signal information; a firstlayer which is formed above said substrate layer and varies in thicknessalong a radial direction; a second layer which is formed above saidfirst layer and varies in thickness along the radial direction; aprotection layer which is formed above said second layer; and a signalrecording layer formed between said substrate layer and said firstlayer, wherein the thickness of said second layer varies opposite to thethickness of said first layer along the radial direction, and said firstlayer and said second layer form an isolation layer, and said firstlayer and said second layer together form a uniform thickness along theradial direction.
 2. The multi-layer optical information recordingmedium of claim 1, further comprising a further signal recording layerformed between said second layer and said protection layer.
 3. Amulti-layer optical information recording medium, comprising: asubstrate layer which is capable of holding signal information; a firstlayer which is formed above said substrate layer and varies in thicknessalong a radial direction; a second layer which is formed above saidfirst layer and varies in thickness along the radial direction; aprotection layer which is formed above said second layer; and a signalrecording layer formed between said substrate layer and said firstlayer, wherein the thickness of said second layer varies opposite to thethickness of said first layer along the radial direction, the thicknessat an inner round portion of said first layer is thinner than thethickness at an outer round portion of said first layer, the thicknessat an outer round portion of said second layer is thinner than thethickness at an inner round portion of said second layer, and said firstlayer and said second layer form an isolation layer.
 4. The multi-layeroptical information recording medium of claim 3, wherein said firstlayer and said second layer together form a uniform thickness along theradial direction.
 5. The multi-layer optical information recordingmedium of claim 3, further comprising a further signal recording layerformed between said second layer and said protection layer.
 6. Amulti-layer optical information recording medium, comprising: asubstrate layer which is capable of holding signal information; a firstlayer which is formed above said substrate layer and varies in thicknessalong a radial direction; a second layer which is formed above saidfirst layer and varies in thickness along the radial direction; aprotection layer which is formed above said second layer; and a signalrecording layer formed between said substrate layer and said firstlayer, wherein the thickness of said second layer varies opposite to thethickness of said first layer along the radial direction, the thicknessat an outer round portion of said first layer is thinner than thethickness at an inner round portion of said first layer, the thicknessat an inner round portion of said second layer is thinner than thethickness at an outer round portion of said second layer, and said firstlayer and said second layer form an isolation layer.
 7. The multi-layeroptical information recording medium of claim 6, wherein said firstlayer and said second layer together form a uniform thickness along theradial direction.
 8. The multi-layer optical information recordingmedium of claim 6, further comprising a further signal recording layerformed between said second layer and said protection layer.